I have a simple SqlAlchemy Relationship defined as follows

class User(BaseModel):
    cars = relationship(
        "Car",
        back_populates="user",
        passive_deletes="all",
    )

class Car(BaseModel):
     user_id: Mapped[Optional[uuid.UUID]] = mapped_column(
        ForeignKey("user_id", ondelete="CASCADE"),
        index=True,
    )

My test is run as follows

 @staticmethod
    async def test_car_is_cascade_deleted(
        db, fixture_user, fixture_car
    ):
        user = await fixture_user(). # just a factory that creates a User object and FLUSH
        car = await fixture_car(
            user=user
        )
   
        await db.refresh(car)
        await db.delete(user)
        await db.commit()
        assert await db.get(User, user.id) is None
        assert await db.get(car, car.id) is None # this fails if await db.refresh(car) is not called

As described in the comment, the await db.refresh(car) looks needed to make the
assert await db.get(car, car.id) getting a None value, otherwise an actual object is retrieved.

I also echoed the queries in SqlAlchemy and I clearly see the Delete instructions

DELETE FROM car WHERE car.user_id = %(user_id)s::UUID
2024-07-18 17:48:46,521 INFO sqlalchemy.engine.Engine [generated in 0.00007s] [{'user_id': 'b652d7c5-6328-4725-b276-914264c0064a'}, {'user_id': 'b652d7c5-6328-4725-b276-914264c0064a'}]
2024-07-18 17:48:46,523 INFO sqlalchemy.engine.Engine DELETE FROM user WHERE user.id = %(id)s::UUID {'id': 'b652d7c5-6328-4725-b276-914264c0064a'}

What I didn’t get from SqlAlchemy session management?